Here,
\(\Delta \lambda =\lambda -\lambda _0\)  is the difference between the wavelength, \(\lambda \) , and the rest wavelength of the Mg II line considered,
\(\Delta \lambda _{{\rm LOS}, m}\equiv \lambda _0 V_{{\rm LOS}, m}/c\)  is the shift of wavelength corresponding to the LOS velocity of the cloud of number m, \(V_{{\rm LOS}, m}\)  (\(c\)  is the light speed);
\(T_m\)  and \(V_{{\rm turb}, m}\)  are the temperature and the turbulent velocity of the cloud of number m, respectively;
\(k_{\rm B}\)  is the Boltzmann constant;
\(m_{\rm Mg}\)  is the atomic mass of magnesium ([1]}; [2]}).
Combining the equation (REF ) of \(m=1\)  and the one of \(m=2\) , the total observed
intensity \(I_2(\Delta \lambda )\)  emitted by two clouds is given by the relation:
\(\begin{aligned}I_2(\Delta \lambda )=I_0(\Delta \lambda ){\rm e}^{-\tau _1(\Delta \lambda )}{\rm e}^{-\tau _2(\Delta \lambda )}+S_1[1-{\rm e}^{-\tau _1(\Delta \lambda )}]{\rm e}^{-\tau _2(\Delta \lambda )}+ S_2[1-{\rm e}^{-\tau _2(\Delta \lambda )}].\end{aligned}\) 
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